Electronic paper is expected to become rapidly popular for use from this time forward. The electronic paper is capable of storing display images even with no power supply, and electrically rewriting display contents. The electronic paper has been under study for implementing a super-low power consumption allowing memory display even if power is turned off, reflective display easy on eyes, and a flexible low-profile display body being flexible like paper. Such electronic paper is considered a possible option for use as a display section of electronic book, electronic newspaper, electronic poster, and others.
The electronic paper is applicable to various display modes including an electrophoresis mode, a twist-ball mode, an organic EL (electroluminescence) display mode, a liquid crystal display mode, and others. The electrophoresis mode is to move electrically-charged particles in the air or in a liquid. The twist-ball mode is to rotate electrically-charged particles colored in two colors. The organic EL display mode is of the self-luminous type with a plurality of organic thin films sandwiched by a cathode and an anode. The liquid crystal display mode is of the no-self-luminous type with a liquid crystal layer sandwiched between a pixel electrode and an opposing electrode.
The research and development for the electronic paper in the liquid crystal display mode has been conducted using a cholesteric liquid crystal material, which is with the selective reflection featuring the bistability utilizing interference reflection of the liquid crystal layer. Herein, the bistability denotes properties with which the liquid crystal material depicts the stability in two different states of orientation. The cholesteric liquid crystal material has properties of being able to remain in two stable states of planer and focal conic for a long time even after the removal of electric field. With the cholesteric liquid crystal material as such, an incident light is interference-reflected thereby in the planer state, and the incident light passes therethrough in the focal conic state. With such properties, a liquid crystal display panel whose liquid crystal layer is made of the cholesteric liquid crystal material can display the contrast of light by selectively reflecting the incident light in the liquid crystal layer, thereby not requiring a polarizing plate any more. Note here that the cholesteric material is also called chiral nematic liquid crystal material.
The liquid crystal display mode using such a cholesteric liquid crystal material (hereinafter, referred to as “cholesteric liquid crystal mode” for convenience) is extremely advantageous in view of color display of liquid crystal display elements. The cholesteric liquid crystal mode utilizes the interference of the liquid crystal material to reflect lights of any predetermined color. This thus enables color display in the cholesteric liquid crystal mode only by laminating liquid crystal display panels reflecting lights of various colors. As such, the cholesteric liquid crystal mode is completely outperforming the other modes described above, i.e., electrophoresis mode and others, in view of color display. For color display, the remaining other modes are all required to use a color filter colored in three colors on a pixel basis, and thus the lightness of color in these modes is about ⅓ of that in the cholesteric liquid crystal mode. In consideration thereof, for such remaining other modes, increasing the lightness is a high hurdle to implement the electronic paper.
As described above, the cholesteric liquid crystal mode is considered a promising mode for the electronic paper capable of color display. The concern here is that, however, for implementing color display, the cholesteric liquid crystal mode is with a three-layered liquid crystal display panel for display of images of red (R), green (G), and blue (B). Such a three-layered liquid crystal display panel is configured by laminating three pieces of liquid crystal display panels, and with such a configuration of laminating three pieces of liquid crystal display panels, the cholesteric liquid crystal mode thus has to overcome the problems such as the large number of components, the complexity of manufacturing process, and the reliability of panel lamination.
FIG. 17 is a schematic diagram illustrating the cross-sectional configuration of a previous color-display cholesteric liquid crystal display element 100. In FIG. 17, for easy understanding, scanning electrode substrates 109b, 109g, and 109r are depicted with 90-degree rotation. FIGS. 18A and 18B each depict an exemplary connection state between a B-use liquid crystal display panel 103b and a display control circuit substrate 131. The B-use liquid crystal display panel 103b here is the one provided to the liquid crystal display element 100 of FIG. 17 together with other R- and G-use liquid crystal display panels 103r and 103g. Specifically, FIG. 18A depicts the B-use liquid crystal display panel 103b viewed from the display surface side, and FIG. 18B depicts the cross section of the B-use liquid crystal display panel 103b cut along a line A-A of FIG. 18A.
As depicted in FIG. 17, the liquid crystal display element 100 is of a configuration including three single-color display panels laminated together, i.e., B-, G-, and R-use liquid crystal display panels 103b, 103g, and 103r, and a black no-light-transmission layer 119 on the rear surface of the R-use liquid crystal display panel 103r. The B- and G-use liquid crystal display panels 103b and 103g are fixedly laminated together by an adhesive layer 117, and the G- and R-use liquid crystal display panels 103g and 103r are fixedly laminated together by another adhesive layer 117.
As depicted in FIGS. 17, 18A and 18B, the B-use liquid crystal display panel 103b is configured to include a scanning electrode substrate 109b, a data electrode substrate 111b, and a cholesteric liquid crystal layer, i.e., the B-use liquid crystal layer 105b. The scanning electrode substrate 109b includes a plurality of scanning electrodes 121b, and the data electrode substrate 111b includes a plurality of data electrodes 123b. The cholesteric liquid crystal layer has a function of wavelength selective reflection, and is sealed between the substrates 109b and 111b with a thickness of several μm. The substrates 109b and 111b are each made of glass or film. When the substrates 109b and 111b are each made of flexible film, the flexibility may change the thickness of the B-use liquid crystal layer 105b, thereby possibly deteriorating the display quality. In order to prevent such deterioration of the display quality due to the substrates 109b and 111b being flexible, the B-use liquid crystal display panel 103b is provided with a plurality of wall structure bodies 115b that are formed adhesive between the substrates 109b and 111b. Such wall structure bodies are described in Patent Document 1 (pamphlet of WO06/100713), for example.
The scanning electrodes 121b and the data electrodes 123b are each extended and exposed, i.e., one end portion thereof, to the outside of a liquid crystal sealing layer, thereby serving as an external connection terminal. The liquid crystal sealing layer here is a display area enclosed by a sealing material 113b. Generally, the external connection terminals of the scanning electrodes 121b are respectively connected to connection terminals (not depicted) of an FPC (Flexible Printed Substrate) 125b via an ACF (Anisotropic Conductive Film) 149. The FPC 125b is mounted with a liquid-crystal drive IC (Integrated Circuit) 135b for driving the scanning electrodes. From the liquid-crystal drive IC 135b toward the connection terminals of the FPC 125b, leads 147b are wired as many as the scanning electrodes 121b. 
The external connection terminals of the data electrodes 123b are respectively connected to connection terminals of an FPC 127b via an ACF 137. The FPC 127b is mounted with a liquid-crystal drive IC 133b for driving the data electrodes. From the liquid-crystal drive IC 133b toward the connection terminals of the FPC 127b, leads 143b are wired as many as the data electrodes 123b. The B-use liquid crystal display panel 103b is connected to the outside generally at two portions of the scanning electrodes 121b and the data electrodes 123b. 
The liquid-crystal drive IC 135b mounted on the FPC 125b is connected to an input signal line 145b including power-supply wiring, data wiring, and clock-signal wiring, for example. The input signal line 145b is connected to, using a solder material 139, an external terminal on the display control circuit substrate 131 carrying thereon a control IC, and a power supply circuit (both not depicted), for example. The liquid-crystal drive IC 133b provided on the FPC 127b is connected to an input signal line 141b including power-supply wiring, data wiring, and clock-signal wiring, for example. The input signal line 141b is connected to, using the solder material 139, an external terminal on the display control circuit substrate 131. The solder material 139 is surely not restrictive, and a socket may be alternatively used for connection of the FPCs 125b and 127b as such.
In FIG. 17, the G- and R-use liquid crystal display panels 103g and 103r are each in the configuration same as that of the B-use liquid crystal display panel 103b, and are each connected to the display control circuit substrate 131.
FIGS. 19A and 19B are each a schematic diagram illustrating the cross section of the liquid crystal display panel 103 connected with an FPC. For implementing color display, as depicted in FIG. 17, there needs to laminate together the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b. As depicted in FIG. 19A, in a previous general technology (hereinafter, referred to as “first previous technology”), the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b are respectively provided with data electrodes 123r, 123g, and 123b, which are connected to FPCs 127r, 127g, and 127b via ACFs 137r, 137g, and 137b, respectively. The FPCs 127r, 127g, and 127b here are those respectively carrying thereon liquid-crystal drive ICs 133r, 133g, and 133b. Also in the first previous technology, as depicted in FIG. 19B, the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b are respectively provided with scanning electrodes 121r, 121g, and 121b, which are connected to FPCs 125r, 125g, and 125b via ACFs 149r, 149g, and 149b, respectively. The FPCs 125r, 125g, and 125b here are those carrying no liquid-crystal drive IC. The liquid crystal display element 100 is configured first by respectively connecting the FPCs 127r, 127g, and 127b, and the FPCs 125r, 125g, and 125b to the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b, and then laminating the resulting three panels together. Thereafter, as depicted in FIG. 19B, the FPCs 125r, 125b, and 125g are respectively connected to, via ACFs 157r, 157g, and 157b, to a wiring pattern 155 formed to the FPCs 125 provided with the liquid-crystal drive ICs 135. The FPCs 125r, 125g, and 125b for the scanning electrodes and the FPCs 127r, 127g, and 127b for the data electrodes are each connected to the display control circuit substrate 131 (refer to FIGS. 18A and 18B) provided thereon with a control circuit, and others.
The liquid crystal display element 100 is a small-sized display element with which the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b can be driven only by the liquid-crystal drive ICs 133r, 133g, and 133b, respectively. However, although being small in size, the liquid crystal display element 100 has to establish therein nine connections in total before and after the panel lamination, i.e., six connections between the R-, G-, and B-use liquid crystal display panels 103r, 103g, and 103b to the FPCs 125r, 125g, 125b, 127r, 127g, and 127b, and three connections between the FPCs 125r, 125g, and 125b to the FPC 125. What is more, the liquid crystal display element 100 needs seven FPCs, and four liquid-crystal drive ICs, i.e., requires a large number of components. If the liquid crystal display element becomes large in size, a plurality of drive ICs are additionally required for driving the R-, G-, and B-use liquid crystal display panels, and this means the additional increase of the number of connections between the liquid crystal display panels and the FPCs. With such an additional increase of the number of connections, the resulting liquid crystal display element is reduced in reliability. The concern here is that, in the multi-layer liquid crystal display element, the configuration with a fewer number of FPCs is not yet implemented. As such, because no such configuration with a fewer number of connections is yet realized, the multi-layer liquid crystal display element costs a lot for the material and in terms of man-hours, and the reliability thereof is also reduced.
FIG. 20 is a flowchart of a general manufacturing process of a previous multi-layer liquid crystal display element using a film substrate. FIGS. 21A to 21D are schematic diagrams illustrating how such a previous multi-layer liquid crystal display element using a film substrate is manufactured. Specifically, FIG. 21A is a diagram for illustrating the manufacturing process of step S1 of FIG. 20, and FIGS. 21B to 21D are the diagrams for illustrating the manufacturing processes of steps S2 to S11 of FIG. 20.
As depicted in FIGS. 20 and 21A, a roll-like upper film substrate 161 is formed thereon with a transparent conductor like a stripe extending in the longitudinal direction of the upper film substrate 161 so that upper substrate electrodes 163 are formed (step S1). The upper substrate electrode 163 is formed with a plurality of electrode patterns on the upper film substrate 161. Also a roll-like lower film substrate (not depicted) is formed thereon with a transparent conductor like a stripe extending in the latitudinal direction of the lower film substrate so that lower substrate electrodes are formed (step S2). The upper substrate electrodes 163 are so disposed as to intersect with the lower substrate electrodes when the upper film substrate 161 is laminated together with the lower film substrate.
Next, in accordance with the final dimension of the liquid crystal display panels, and the number of panels to be needed, the upper film substrate 161 is cut to the size of a sheet-like substrate 165 of FIG. 21B, a strip-like substrate 167 of FIG. 21C, or a small-piece substrate 169 of FIG. 21D (step S3). Thereafter, to an area formed with the upper substrate electrodes 163, a column-like spacer is formed with a thickness of several microns for making uniform the thickness of liquid crystal display cells (step S4). The lower film substrate is then cut to any of the sizes of the sheet-like substrate, the strip-like substrate, and the small-piece substrate of FIGS. 21B to 21D (step S5). When the upper film substrate 161 is cut to the size of the sheet-like substrate 163, for example, the lower film substrate is accordingly cut to the size of the sheet-like substrate (step S5). As such, the lower film substrate is cut to the same size as the upper film substrate 161. Next, to the area formed with the lower substrate electrodes, spherical spacers are dispersed to keep uniform the thickness of the liquid crystal display cells (step S6). A sealing material (not depicted) is then formed to enclose the area formed with the upper substrate electrodes 163 for sealing the liquid crystal material therein (step S7). Alternatively, the sealing material may be formed to enclose the lower substrate electrodes. The upper and lower substrates are then attached together in the state that the upper and lower substrate electrodes are being intersected with each other, and the column-like spacer and the sealing material are being sandwiched between the substrates. After the attaching of the substrates as such, empty cells are formed (step S8).
From an injection port of each of the empty cells, an R-use liquid crystal material is injected by vacuum injection, for example, for selectively reflecting lights of red (step S9). After the completion of the injection of the R-use liquid crystal material, the injection ports are sealed by an end sealing agent (step S10). When the upper and lower film substrates are both cut into the size of the sheet- or strip-like substrate in steps S3 and S5, the resulting substrate structure is cut to the size of the small-piece substrate of FIG. 21D (step S11). In step S11, the upper substrate electrodes 163 are exposed from the cut end portion of the upper substrate, and the lower substrate electrodes are exposed from the cut end portion of the lower substrate. The concern here is that, because the liquid crystal layer is with the thickness of several microns, it is difficult to cut the upper and lower substrates without damaging the upper substrate electrodes 163 and the lower substrate electrodes. In consideration thereof, the upper and lower substrates may be provided with a cut or formed with an aperture in advance, or the upper and lower film substrates may be cut in advance to the size of not the sheet- and stripe-like substrates of FIGS. 21B and 21C but the size of the small-piece substrate of FIG. 21D. Thereafter, with the exposed portions of the upper substrate electrodes 163 and those of the lower substrate electrodes serving each as a connection terminal, the FPCs are connected thereto using the ACF so that the R-use liquid crystal display panel (single-color panel R) is completed (steps S12 and S13). Note here that the FPCs may be each provided thereon with a liquid-crystal drive IC or may not.
For manufacturing a liquid crystal display element capable of color display, with the manufacturing process similar to those of steps S1 to S13, a G-use liquid crystal display panel (single-color panel G) is formed with an FPC connected thereto (step S14). In step S14, a G-use liquid crystal material is used for selectively reflecting lights of green. Thereafter, with the manufacturing processes similar to those of steps S1 to S13, a B-use liquid crystal display panel (single-color panel B) is formed with an FPC connected thereto (step S15). In step S15, a B-use liquid crystal material is used for selectively reflecting lights of blue.
Based on an alignment mark formed to each of the R-, G-, and B-use liquid crystal display panels, these liquid crystal display panels are positioned for matching of the panels, i.e., the layers, and are laminated together using a photocurable adhesive agent, for example (step S16). In step S16, for example, the R- and G-use liquid crystal display panels are laminated together, and then the B-use liquid crystal display panel is laminated on the G-use liquid crystal display panel. In step S16, as an alternative to the photocurable adhesive agent, an adhesive film, may be used. After the completion of the lamination of the R-, G-, and B-use liquid crystal display panels as such, as depicted in FIG. 19A, the lower substrate electrodes, i.e., the data electrodes, of the R-, G-, and B-use liquid crystal display panels are connected to the display control circuit substrate 131 (refer to FIGS. 18A and 18B) via the respective FPCs using a solder material (step S17). Then in step S17, as depicted in FIG. 19B, the upper substrate electrodes, i.e., scanning electrodes, of the R-, G-, and B-use liquid crystal display panels are connected to a relay substrate via the respective ACFs, and then the relay substrate is soldered to the display control circuit substrate 131 (refer to FIGS. 18A and 18B). The relay substrate here is the one provided thereon with the liquid-crystal drive ICs 135 (scanning drive ICs). By going through such a manufacturing process, completed is a multi-layer liquid crystal display element capable of color display with a narrow frame (step S18).
With the manufacturing processes for the previous multi-layer liquid crystal display element of FIG. 20, not to cover the exposed portions of the upper- and lower-substrate electrodes, the liquid crystal display panels are connected to, before being laminated together, the FPCs by ACF-terminal junction, and then the three liquid crystal display panels are laminated together. After the completion of the lamination as such, the FPCs are connected to the display control circuit substrate or to the relay substrate by ACF-terminal junction. As such, the manufacturing processes for the previous multi-layer liquid crystal display element have the problem of repeating the process of ACF-terminal junction. What is more, the FPC-connected liquid crystal display panels are difficult to handle, and often cause product failure such as lamination misalignment, adhesive stain, and poor junction at FPC-terminal-junction portions, and others. Also with the manufacturing processes described above, the liquid crystal display panels are laminated together after being respectively connected to the FPCs, and thus multiple production with such a lamination process is not possible. On the other hand, in the manufacturing processes for the previous liquid crystal display element, because a failure check is performed at the manufacturing stage of the single-color liquid crystal display panels, there are advantages of achieving the product yields being generally high, and implementing a narrower frame for the resulting liquid crystal display panels.
Patent Document 2 (JP-A-2001-306000) describes a method for preventing repetition of process execution, i.e., display panels are first stacked together, and then are connected all at once. With the method described in Patent Document 2 (hereinafter, referred to as “second previous technology”), a height-different exposed portion is provided to the laminate of the display panels at their connection portions, and after the lamination of the display panels as such, the FPCs are respectively connected to the display panels. Such a method requires, however, a crimp area to each of the panel layers with a width of about several millimeters for securing the reliability of the ACF-connection. This thus arises a problem of substantially increasing the frame area that has nothing to do with display. What is more, because the three types of R-, G-, and B-use display panels are different in size, there is another problem of a difficulty in so-called multiple production with a plurality of panels aligned. As such, there has been a demand for the configuration and method allowing a narrow frame of a display panel, an FPC-wiring connection after display panel lamination, a fewer number of components and connection points, and lamination leading to multiple production.